Coding techniques are generally used when a large amount of image information is first compressed and then coded to be transmitted or stored. One method of compressing the information involves dividing the whole image into small blocks. In this case, the compressed information consists of information generated in the unit of a pixel (hereinafter, referred to as video information) and information generated in the unit of a block (hereinafter, referred to as header information). Deterioration of the quality of the picture generated by an error in the header information is more severe than that generated by an error in the video information.
There are two types of errors, burst errors and random errors. Generally, random errors can be corrected by error correction coding systems, but burst errors cannot be corrected. Error correction coding systems therefore commonly use a method called shuffling to convert burst errors into random errors.
Generally in this shuffling coding method, all the image information is divided into small blocks (see FIG. 1). Each of these blocks is then compressed into a block code composed of header information and video information (see FIG. 2). These block codes are then coded to be transmitted or stored. If an error is generated when the digital image information is transmitted, stored, received, or reproduced, picture quality of the image deteriorates due to the generated error. Accordingly, an error correction coding technique has been developed to compensate for this problem with the above-described shuffling coding technique. In this error correction technique, in order to correct errors generated during transmitting or storing, or receiving or reproducing of the image information to obtain the original image, parity data is added to the image information before the information is coded. This conventional and known error correction coding method will be described below with reference to FIGS. 3, 4 and 5.
This conventional error correction coding method codes the image information into the form of a map such as the map shown in FIG. 3. As shown in FIG. 3, the compressed and coded block codes are arranged in a vertical direction. Parity data is added in the horizontal and vertical directions. With reference to detailed FIG. 4, the coded image information shown in FIG. 3 consists of header information Hij and video information Dik arranged in parallel in a vertical direction. Horizontal parity data HPil appears to the right side of the video information Dik. Vertical parity data VPm,n+1 is added in the portion below the header and video information Hij and Dik and below the horizontal parity data HPil.
When transmitted or stored, the coded image information shown in FIGS. 3 and 4 is transmitted or stored from up to down and from left to right as shown in FIG. 5 so that a group of header information and a group of video information is formed for transmission. If an error is generated during the process of transmitting or storing, or receiving or reproducing of a digital image, the error is corrected using the parity information HPil and VPm,n+1. Errors which exceed the error correction capability, however, cannot be corrected so they deteriorate the picture. In particular, errors in a header exceeding the error correction capability generally have worse effects on the picture than do errors generated in video information.
Thus, this conventional error correction coding method of FIGS. 3, 4 and 5 codes the information into a group of video information and a group of header information in such a way that burst errors may be generated between header information and also between video information. This conventional coding method therefore does not prevent the severe deterioration of picture quality caused by burst errors.